1. Technical Field of the Invention
The present invention relates generally to alternators and drive systems for automotive vehicles. More particularly, the invention relates to an automotive alternator that is supplied with rotating power from an engine via a belt of a serpentine belt drive system and includes a magnetic fluctuation suppressor for suppressing fluctuations in rotational movement of the alternator.
2. Description of the Related Art
In recent years, the problem of engine noise has been widely addressed; in order to make engines quiet, research on engine vibration control and engine rotation stabilization has been actively conducted.
Typically, in a serpentine belt drive system for an automotive vehicle, an internal combustion engine drives, via a belt, a plurality of auxiliary machines (or accessories) that includes an alternator, an air conditioning compressor, a water pump, and an oil pump (for power steering). In such a system, an unstable behavior of an auxiliary machine that has a large moment of inertia will cause the engine to rotate unstably. Generally, the equivalent moment of inertia of an auxiliary machine is proportional to the square of the speed increasing ratio of the auxiliary machine with respect to the engine. Among the auxiliary machines, the alternator has both a large inertia and a large speed increasing ratio; thus, suppression of fluctuations in rotational movement of the alternator is critical to the stabilization of rotation of the engine.
As an approach to suppress fluctuations in rotational movement of an automotive alternator, theories that have been developed to solve vibration suppression problems can be applied. Specifically, the following two vibration suppression methods can be considered.                Vibration absorption        Vibration isolation        
The first method is to employ a dynamic vibration absorber to absorb vibrations of a target body in a specific resonance area. The dynamic vibration absorber is configured with a weight, which has a mass equal to about one tenth of that of the target body, and an elastic body with a suitable spring rate (or elastic constant). The dynamic vibration absorber is also configured to have a suitable attenuation coefficient.
In the case of applying the first method to an automotive alternator, it is necessary to connect a weight, which has a suitable mass and will accordingly produce a suitable moment of inertia, to a rotor or a rotary shaft of the alternator via a suitable elastic body (e.g., a spring).
The second method is to arrange a vibration isolator in the vibration transfer path from a vibrating body to an associated body, thereby preventing vibrations of the vibrating body from transferring to the associated body.
In the case of applying the second method to an automotive alternator, it is necessary to arrange a fluctuation isolator in the fluctuation transfer path from the alternator to an engine that drives the alternator.
Japanese Patent First Publication No. S61-228153, an English equivalent of which is U.S. Pat. No. 4,725,259, discloses an automotive alternator, in which a one-way clutch is employed to selectively connect or disconnect a rotary shaft and a pulley that is driven by an engine via a belt. The one-way clutch may serve as a fluctuation isolator, which prevents fluctuations in rotational movement of the alternator from transferring to the engine by disconnecting the rotary shaft from the pulley.
Japanese Translation of International Publication No. 2001-523325, an English equivalent of which is U.S. Pat. No. 6,083,130, discloses an automotive alternator, in which a spring and one-way clutch mechanism is employed to connect a rotary shaft and a pulley that is driven by an engine via a belt. The spring and one-way clutch mechanism may serve as a fluctuation isolator, which prevents fluctuations in rotational movement of the alternator from transferring to the engine by absorbing the fluctuations.
However, when a mechanical element, such as a spring and a clutch, is employed to suppress fluctuations in rotational movement of an automotive alternator, a torque for power generation, a torque due to the inertia of the alternator, and a centrifugal force of the mechanical element will act on the connection between a rotor or a rotary shaft of the alternator and the mechanical element. Consequently, if not properly designed and constructed, the connection would be broken, thus resulting in a failure of the alternator, or even the whole drive system.
Accordingly, it is required to carefully design and construct, under durability requirements and dimensional constraints, an automotive alternator that has a mechanical fluctuation suppressor for suppressing fluctuations in rotational movement of the alternator. However, this will increase the number of product types and manufacturing cost of the alternator.